Re: heading toward datatyping telecon

At 10:06 AM 11/3/01 +0000, Brian McBride wrote:


>Pat Hayes wrote:
>
>[...]
>
>
>>Oh, I agree its not helpful to conflate them. But let me probe this other 
>>usage a little. Consider various kinds of numerals, eg decimal, 
>>hexadecimal, octal, binary. Obviously these all have the same value 
>>space, so it doesn't make sense to use something like 'octal number' to 
>>refer to a value space. So I'm left wondering what this usage is supposed 
>>to mean.  For example, what is a decimal *integer* ?
>
>
>Yes, I agree.  That's why I don't expect to see arcs labelled rdf:type 
>with xsd:integer at the sharp end.  I expect rdf:type to identify the 
>class of the node at its blunt end, and I think of the class of the object 
>as identifying its value space, and is independent of its lexical space.
>
>My mental model.  I can change it its wrong; but I don't think its uncommon.

Aha!  I overlooked that.  Now you point it out, I find myself tending to 
agree.  In other contexts, I too would have regarded rdf:type as saying 
something about the value space of the thing at the blunt end, rather than 
its representation.  The mental picture this paints for me is something 
like this:

Given:

DTVS : Data Type Value Space, a set of possible values
DTLS : Data Type Literal Space, a set of strings that can represent things 
in DTVS
DTLV : A mapping from DTLS to DTVS

The "simple" notion of data type would be DTVS, and the "extended" notion 
would be something like <DTVS,DTLS,DTLV>.

Then:

If the rdf:type relational extension value <aaa,DTVS> indicates that aaa is 
a member of DTVS, some different property would be needed whose extension 
could contain <aaa,<DTVS,DTLS,DTLV>>, which would also designate the 
literal space of aaa and its mapping to the value space.

Alternatively, I suppose one could allow that rdf:type indicates the 
extended notion, from which the simple notion could be derived in any 
instance (I think this might require some small re-work of the model theory 
surrounding IEXT and ICEXT).  It might be permitted for DTLS and/or DTLV to 
be undefined, in which case the information provided would be the same as 
in the simple case.  (e.g. plain integer as opposed to "decimal integer".)

I don't know if any of this helps.

FWIW, when I reviewed XML schema data types some time ago, I was deeply 
uncomfortable that the primitive value spaces seemed to be defined (and 
constrained) in terms of their lexical representations.  This seemed maybe 
justified because XML schema was, by design, all about values that were 
represented in a text-based format (i.e. XML).  But I'm not convinced that 
the considerations apply equivalently to RDF.

#g


------------------------------------------------------------
Graham Klyne                    MIMEsweeper Group
Strategic Research              <http://www.mimesweeper.com>
<Graham.Klyne@MIMEsweeper.com>
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Received on Saturday, 3 November 2001 08:59:06 UTC